/*=========================================================================
 *
 *  Copyright RTK Consortium
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 *  you may not use this file except in compliance with the License.
 *  You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0.txt
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 *=========================================================================*/

#ifndef rtkForwardDifferenceGradientImageFilter_h
#define rtkForwardDifferenceGradientImageFilter_h

#include <itkImageToImageFilter.h>
#include <itkCovariantVector.h>
#include <itkImageRegionIterator.h>

#include "rtkMacro.h"

namespace rtk
{
/** \class ForwardDifferenceGradientImageFilter
 * \brief Computes the gradient of an image using forward difference.
 *
 *
 * The second template parameter defines the value type used in the
 * derivative operator (defaults to float).  The third template
 * parameter defines the value type used for output image (defaults to
 * float).  The output image is defined as a covariant vector image
 * whose value type is specified as this third template parameter.
 *
 * The exact definition of the desired gradient filter can
 * be found in Chambolle, Antonin. "An Algorithm for Total
 * Variation Minimization and Applications." J. Math. Imaging Vis. 20,
 * no. 1-2 (January 2004): 89-97.
 *
 * \author Cyril Mory
 *
 * \ingroup RTK
 */

template <typename TInputImage,
          typename TOperatorValueType = float,
          typename TOuputValue = float,
          typename TOuputImage =
            itk::Image<itk::CovariantVector<TOuputValue, TInputImage::ImageDimension>, TInputImage::ImageDimension>>
class ForwardDifferenceGradientImageFilter : public itk::ImageToImageFilter<TInputImage, TOuputImage>
{
public:
#if ITK_VERSION_MAJOR == 5 && ITK_VERSION_MINOR == 1
  ITK_DISALLOW_COPY_AND_ASSIGN(ForwardDifferenceGradientImageFilter);
#else
  ITK_DISALLOW_COPY_AND_MOVE(ForwardDifferenceGradientImageFilter);
#endif

  /** Extract dimension from input image. */
  itkStaticConstMacro(InputImageDimension, unsigned int, TInputImage::ImageDimension);
  itkStaticConstMacro(OutputImageDimension, unsigned int, TOuputImage::ImageDimension);

  /** Standard class type alias. */
  using Self = ForwardDifferenceGradientImageFilter;

  /** Convenient type alias for simplifying declarations. */
  using InputImageType = TInputImage;
  using InputImagePointer = typename InputImageType::Pointer;
  using OutputImageType = TOuputImage;
  using OutputImagePointer = typename OutputImageType::Pointer;

  /** Standard class type alias. */
  using Superclass = itk::ImageToImageFilter<InputImageType, OutputImageType>;
  using Pointer = itk::SmartPointer<Self>;
  using ConstPointer = itk::SmartPointer<const Self>;

  /** Method for creation through the object factory. */
  itkNewMacro(Self);

  /** Run-time type information (and related methods). */
  itkTypeMacro(ForwardDifferenceGradientImageFilter, ImageToImageFilter);

  /** Image type alias support. */
  using OperatorValueType = TOperatorValueType;
  using OutputValueType = TOuputValue;
  using InputPixelType = typename InputImageType::PixelType;
  using CovariantVectorType = typename OutputImageType::PixelType;
  using OutputImageRegionType = typename OutputImageType::RegionType;

  /** ForwardDifferenceGradientImageFilter needs a larger input requested region than
   * the output requested region.  As such, ForwardDifferenceGradientImageFilter needs
   * to provide an implementation for GenerateInputRequestedRegion()
   * in order to inform the pipeline execution model.
   *
   * \sa ImageToImageFilter::GenerateInputRequestedRegion() */
  void
  GenerateInputRequestedRegion() override;

  /** Use the image spacing information in calculations. Use this option if you
   *  want derivatives in physical space. Default is UseImageSpacingOn. */
  void
  SetUseImageSpacingOn()
  {
    this->SetUseImageSpacing(true);
  }

  /** Ignore the image spacing. Use this option if you want derivatives in
      isotropic pixel space.  Default is UseImageSpacingOn. */
  void
  SetUseImageSpacingOff()
  {
    this->SetUseImageSpacing(false);
  }

  /** Set/Get whether or not the filter will use the spacing of the input
      image in its calculations */
  itkSetMacro(UseImageSpacing, bool);
  itkGetConstMacro(UseImageSpacing, bool);

  /** Set along which dimensions the gradient computation should be
      performed. The vector components at unprocessed dimensions contain
      undetermined values */
  void
  SetDimensionsProcessed(bool * DimensionsProcessed);

  /** Allows to change the default boundary condition */
  void
  OverrideBoundaryCondition(itk::ImageBoundaryCondition<TInputImage> * boundaryCondition);

#ifdef ITK_USE_CONCEPT_CHECKING
  // Begin concept checking
  itkConceptMacro(InputConvertibleToOutputCheck, (itk::Concept::Convertible<InputPixelType, OutputValueType>));
  itkConceptMacro(OutputHasNumericTraitsCheck, (itk::Concept::HasNumericTraits<OutputValueType>));
  // End concept checking
#endif

  /** The UseImageDirection flag determines whether image derivatives are
   * computed with respect to the image grid or with respect to the physical
   * space. When this flag is ON the derivatives are computed with respect to
   * the coodinate system of physical space. The difference is whether we take
   * into account the image Direction or not. The flag ON will take into
   * account the image direction and will result in an extra matrix
   * multiplication compared to the amount of computation performed when the
   * flag is OFF.
   * The default value of this flag is On.
   */
  itkSetMacro(UseImageDirection, bool);
  itkGetConstMacro(UseImageDirection, bool);
  itkBooleanMacro(UseImageDirection);

protected:
  ForwardDifferenceGradientImageFilter();
  ~ForwardDifferenceGradientImageFilter() override;
  void
  PrintSelf(std::ostream & os, itk::Indent indent) const override;

  /** ForwardDifferenceGradientImageFilter can be implemented as a multithreaded filter.
   * Therefore, this implementation provides a ThreadedGenerateData()
   * routine which is called for each processing thread. The output
   * image data is allocated automatically by the superclass prior to
   * calling ThreadedGenerateData().  ThreadedGenerateData can only
   * write to the portion of the output image specified by the
   * parameter "outputRegionForThread"
   *
   * \sa ImageToImageFilter::ThreadedGenerateData(),
   *     ImageToImageFilter::GenerateData() */
  void
  DynamicThreadedGenerateData(const OutputImageRegionType & outputRegionForThread) override;

  void
  GenerateOutputInformation() override;

private:
  //  // An overloaded method which may transform the gradient to a
  //  // physical vector and converts to the correct output pixel type.
  //  template <typename TValue>
  //  void SetOutputPixel( ImageRegionIterator< VectorImage<TValue,OutputImageDimension> > &it, CovariantVectorType
  //  &gradient )
  //  {
  //    if ( this->m_UseImageDirection )
  //      {
  //      CovariantVectorType physicalGradient;
  //      it.GetImage()->TransformLocalVectorToPhysicalVector( gradient, physicalGradient );
  //      it.Set( OutputPixelType( physicalGradient.GetDataPointer(), InputImageDimension, false ) );
  //      }
  //    else
  //      {
  //      it.Set( OutputPixelType( gradient.GetDataPointer(), InputImageDimension, false ) );
  //      }
  //  }

  template <typename T>
  void
  SetOutputPixel(itk::ImageRegionIterator<T> & it, CovariantVectorType & gradient)
  {
    it.Value() = gradient;
  }


  bool m_UseImageSpacing;

  // flag to take or not the image direction into account
  // when computing the derivatives.
  bool m_UseImageDirection;

  // list of the dimensions along which the gradient has
  // to be computed. The components on other dimensions
  // are set to zero
  bool m_DimensionsProcessed[TInputImage::ImageDimension];

  itk::ImageBoundaryCondition<TInputImage, TInputImage> * m_BoundaryCondition;
  bool                                                    m_IsBoundaryConditionOverriden;
};
} // namespace rtk

#ifndef ITK_MANUAL_INSTANTIATION
#  include "rtkForwardDifferenceGradientImageFilter.hxx"
#endif

#endif
